The topics that have been studied in cryptography field include a Chosen Ciphertext Attacks (CCA)-secure cryptographic scheme. Recently, the studies of the CCA-secure cryptographic scheme based on an identity-based encryption (IBE) scheme (refer to non-patent literature 1, for example), which is usually Chosen Plaintext Attacks (CPA) secure, have become active. In non-patent literature 2, for example, a CHK transformation method is proposed. In the CHK transformation method, a one-time signature scheme is used to build the CCA-secure cryptographic scheme based on the CPA-secure IBE scheme. In non-patent literature 3, for example, a BK transformation method is proposed. In the BK transformation method, a message authentication code (MAC) and a bit commitment scheme are used to build the CCA-secure cryptographic scheme based on the CPA-secure IBE scheme.